Aerosols are increasingly being used for delivering medication for therapeutic treatment of the lungs as well as systemic delivery of therapeutic agents. For example, in the treatment of asthma, inhalers are commonly used for delivering bronchodilators such as β2 agonists and anti-inflammatory agents such as corticosteroids. Two types of inhalers are in common use, pressurized metered dose inhalers (pMDIs) and dry powder inhalers (DPIs). Both types of inhalers have as their object the delivery of medication (which is typically in the form of a solid particulate or powder) into the airways of the lungs at the location of the condition being treated or for systemic delivery.
In a traditional pMDI device, the medication is provided in a pressurized aerosol canister, with the medication being suspended or dissolved in a liquid propellant such as a chlorofluorocarbon (CFC) or hydrofluoroalkane (HFA). The canister includes a metering valve having a hollow discharge stem which can be depressed inward against an internal spring. Once the discharge stem is fully depressed into the canister a metered volume of propellant-medication mixture is discharged through the stem. The discharge is in the form of an aerosol comprising fine droplets of propellant in which particles of the medication are suspended or dissolved. A typical pMDI for use with such a canister includes a housing having an actuator and a nozzle. The canister is inserted into the housing with the hollow discharge stem of the canister being received in a bore in the actuator. Depressing the closed end of the canister causes the stem to be pushed inward into the canister so that a metered volume of medication is discharged through the nozzle. The housing further defines a flowpath in fluid communication with the nozzle, with the flowpath having an outlet at a mouthpiece portion of the housing, such that the aerosolized medication may be inhaled after it exits the mouthpiece portion. The patient either inserts the mouthpiece into the mouth with the lips closed around the mouthpiece, or holds the mouthpiece at a slight distance away from an open mouth. The patient then depresses the canister to discharge the medication, and simultaneously inhales.
In the field of inhalers, it is known to use a dose counter for tracking and/or displaying the number of doses that have been dispensed or that remain to be dispensed from the inhaler. Such conventional counters are generally incremented each time a drug dose is expelled by the inhaler.
In addition, there exists a need to inactivate the inhaler in order to prevent a patient from delivering more than the required number of doses. For standard pills or tablets, only the actual number of doses prescribed by the physician are dispensed by the pharmacist. For an inhaler the problem is far more complicated. It isn't practical to limit the number of doses by limiting the amount of propellant/drug in the canister because then the last few actuations of the inhaler would only deliver a partial dose. Thus there is a need to be to able to inactivate the inhaler while there is still sufficient content in the canister to provide for the full amount of drug delivery for each of the actuations of the inhaler.
In addition it may be difficult from a manufacturing perspective to properly fill the canister with a de minimus amount of medicament. Thus from a quality control perspective, it is better to fill the canister with an amount that permits reproducible filling and then limit the number of doses by use of the counter/lockout mechanism of the present invention.
The disclosed invention was developed to correct the above-described problem. The disclosed invention of a dose counter/lockout mechanism is shown incorporated into an inhaler having a pMDI medication canister, a synchronized breath-actuated trigger, and a flow control chamber. However, the disclosed dose counter/lockout mechanism could be incorporated into a inhaler in which the canister actuation is done manually.
Furthermore, the disclosed inhaler includes a dose counter that increments only after an actual delivery of drug from the medication canister as occurs when the canister is depressed beyond a certain point. Upon reaching a predetermined number of actuations two things occur. One is that the dose counting wheel can no longer be incremented. Secondly, a spring assembly, which needs to be cocked (i.e. compressed) in order to depress and therefore discharge medicament from the canister, is disengaged from the rest of mechanism and therefore can't be compressed and therefore can't cause the medicament canister deliver a dose.